Obesity, an insulin-resistant state, is a major risk factor for type 2 diabetes. Increased expression and activity of protein tyrosine phosphatase 1B (PTP1B) are observed in muscle and adipose tissue of obese, insulin-resistant animals and humans, and have been implicated in causing insulin resistance. Transgenic PTP1B overexpression in skeletal muscle of mice is sufficient to impair muscle insulin action and cause whole-body insulin-resistance. Conversely, PTP1B-deficient mice have increased insulin sensitivity in muscle and liver. PTP1B also regulates leptin action; PTP1B-deficient mice have reduced adiposity due to increased leptin sensitivity in hypothalamus. Preliminary data show that PTP1B is overexpressed in multiple insulin- and leptin-target tissues of obese mice, including the hypothalamus. To determine whether PTP1B overexpression in other insulin- and leptin-target tissues contributes to insulin- and leptin-resistance in vivo, the proposed studies will generate mice in which transgenic PTP1B overexpression is conditionally regulated by tissue-specific co-expression of Cre recombinase. This animal model will provide a powerful tool to determine the effects of PTP1B overexpression in multiple insulin- and leptin-responsive tissues and cell types of interest. To determine whether PTP1B action on insulin and/or leptin signaling in hypothalamus regulates adiposity in vivo, we will generate transgenic mice overexpressing PTP1B selectively in POMC and AGRP/NPY neurons in the arcuate nucleus of hypothalamus, by breeding conditional PTP1B overexpressing mice to mice expressing Cre recombinase selectively in POMC and/or AGRP neurons. Determining whether PTP1B overexpression in arcuate nucleus of hypothalamus negatively regulates insulin-sensitivity and increases adiposity will provide important insights into understanding of how PTP1B overexpression negatively regulates insulin and leptin action in vivo, contributing to the development of insulin resistance, obesity, and type 2 diabetes. [unreadable] [unreadable]